Data transmissions in LTE in both the uplink and the downlink directions are controlled by the network. This is similar to other technologies such as GSM and UMTS. In these systems, some or all of the scheduling control is located in centralized network components such as the PCU (see Chapter 2) or the RNC (see Chapter 3). In LTE, the scheduling is fully controlled by the eNode-Bs as higher layer radio network control instances were removed from the overall network design. Some of the advantages of network-based scheduling are as follows:
- The network can react to changing radio conditions of each user and optimize the overall throughput.
- The network can ensure the QoS for each user.
- Overload situations can be dealt with.
Other technologies such as Wi-Fi do not use centralized control and leave it to the devices communicating in the network to cooperatively use the air interface. Here, central control is not necessary as the number of devices simultaneously communicating over a Wi-Fi access point is much lower and the coverage area is much smaller. Details are discussed in Chapter 5.
4.5.1 Downlink Scheduling
In the downlink direction, the eNode-B's scheduler is responsible for forwarding the data that it receives from the network, for all users it serves, over the air interface. In practice, a single logical default bearer is usually assigned to a mobile device, over which the data is transported. To ensure QoS for applications such as VoIP via the IMS (see Chapter ...